Method for increasing the diameter of an ink jet ink dot

ABSTRACT

A method for increasing the diameter of an ink jet ink dot resulting from the application of an ink jet ink drop applied to the surface of an ink jet recording medium having a support having thereon an image-receiving layer, the image-receiving layer containing: a) from about 20 to about 65% by volume of particles; b) from about 25 to about 70% by volume of a polymeric binder; and c) up to about 10% by volume of a cross-linking agent; the method comprising applying the ink jet ink drop on the surface of the image-receiving layer whereby the diameter of the ink jet ink dot is increased relative to that which would have been obtained if the image-receiving layer had greater than about 65% by volume of particles.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 10/324,847, filedDec. 20, 2002 now U.S. Pat. No. 6,945,647 entitled “Method ForIncreasing The Diameter Of An Ink Jet Ink Dot” by Kwok L. Yip et al.

Reference is made to the following commonly assigned, U.S. patent andco-pending U.S. patent application, respectively:

-   -   U.S. Pat. No. 6,634,743 by Perchak et al., issued Oct. 21, 2003        entitled “Method For Increasing the Diameter of an Ink Jet Ink        Dot”; and    -   Application Ser. No. 10/324,483 by Yip et al., filed Dec. 20,        2002 entitled “Ink Jet Recording Element.”

FIELD OF THE INVENTION

The present invention relates to a method for increasing the diameter ofan ink jet ink dot.

BACKGROUND OF THE INVENTION

In a typical ink jet recording or printing system, ink droplets areejected from a nozzle at high speed towards a recording element ormedium to produce an image on the medium. The ink droplets, or recordingliquid, generally comprise a recording agent, such as a dye or pigment,and a large amount of solvent. The solvent, or carrier liquid, typicallyis made up of water and an organic material such as a monohydricalcohol, a polyhydric alcohol or mixtures thereof.

An ink jet recording element typically comprises a support having on atleast one surface thereof an ink-receiving or image-receiving layer, andincludes those intended for reflection viewing, which have an opaquesupport, and those intended for viewing by transmitted light, which havea transparent support.

An important characteristic of ink jet recording elements is their needto dry quickly after printing. To this end, porous recording elementshave been developed which provide nearly instantaneous drying as long asthey have sufficient thickness and pore volume to effectively containthe liquid ink. For example, a porous recording element can bemanufactured by cast coating, in which a particulate-containing coatingis applied to a support and is dried in contact with a polished smoothsurface.

When an ink drop contacts the ink jet recording medium, the dropinitially spreads on the surface and then begins to adsorb into themedium. The ink adsorbs vertically into the medium as well as radially.The rate of ink adsorption depends on the nature of the medium. Inkadsorption in non-porous media comprising hydrophilic polymers takesplace due to molecular diffusion and occurs at a much slower rate thanfor porous media where the ink adsorption occurs due to capillaryaction. The adsorption of the ink drop transports a colorant into themedium to form the image.

The diameter of the resulting colorant in the medium is referred to asdot size. Dot size is an important parameter in ink jet printing systemsand is a key component in establishing image quality and printerproductivity. Smaller dot sizes yield a gain in edge acuity but decreaseprinter productivity. Larger dot sizes can cover up for printing errorsdue to misplaced drops. Therefore, the ability to control dot size is animportant issue for ink jet printing systems.

Dot gain refers to the increase in dot size over the initial, sphericaldrop diameter. The dot gain is determined by the ratio of the final dotdiameter on the recording medium to the initial drop diameter. Thedesired dot size is typically achieved by controlling the drop volume,i.e., larger volume drops produce larger dot sizes in the medium. Itwould be desirable to find a way to increase dot size without having toincrease drop volume.

U.S. Pat. No. 6,114,022 relates to a method for controlling the dotdiameter on an ink jet receptive medium that employs a microporousmedium and a porous imaging layer. The dot gain achieved by this processis about 3.5. However, there are problems with this method in that theamount of dot gain is not as large as one would like and the process islimited to pigmented inks.

It is an object of this invention to provide a method for increasing thedot gain of an ink jet ink drop applied to an ink jet recording elementin an amount of up to about 15. It is another object of the invention toprovide a method for increasing the diameter of an ink jet ink dotresulting from the application of an ink jet ink drop wherein the inkjet ink comprises a dye.

SUMMARY OF THE INVENTION

These and other objects are achieved in accordance with the inventionwhich comprises a method for increasing the diameter of an ink jet inkdot resulting from the application of an ink jet ink drop applied to thesurface of an ink jet recording medium comprising a support havingthereon an image-receiving layer, the image-receiving layer containing:

-   a) from about 20 to about 65% by volume of particles;-   b) from about 25 to about 70% by volume of a polymeric binder; and-   c) up to about 10% by volume of a cross-linking agent;    the method comprising applying the ink jet ink drop on the surface    of the image-receiving layer whereby the diameter of the ink jet ink    dot is increased relative to that which would have been obtained if    the image-receiving layer had greater than about 65% by volume of    particles.

By use of the method of the invention, the dot gain of an ink jet inkdrop applied to an ink jet recording element can be in an amount of upto about 15 and the ink jet ink can comprise a dye.

Another advantage of the invention is that a smaller volume of ink jetink drops can be used to achieve dot sizes equivalent to those obtainedwith larger volume drops. This results in increased printer productivitysince fewer dots are needed to cover an area of the recording medium,and the drying times are faster.

When the volume percentage of particles in the image-receiving layer ismore than about 65%, the imaging layer behaves like a porous medium inwhich the absorption of ink is due to the capillary pressure of thepores. Typical dot gain for a porous receiver is about 2.0. As thevolume percentage of particles is reduced from about 65%, the binderwill swell upon the absorption of ink and plug the pores near thereceiver surface. This impedes further penetration of ink into themedium and allows more time for the drop to move laterally on thereceiver surface, resulting in a much larger dot gain than a typicalporous receiver. On the other hand, when he volume percentage of thebinder is more than 70%, the image-receiving layer behaves like anon-porous medium in which the absorption of ink is by moleculardiffusion. In this case, the dot gain would become about 2.0 to 3.0 fora typical non-porous receiver. In general, the volume percentage of acomponent in a mixture can be calculated from the given weightpercentage of the components. As an example, for a binary mixture, thevolume percentage of each component is given by

${v_{1} = \frac{\rho_{2}w_{1}}{{\rho_{2}w_{1}} + {\rho_{1}w_{2}}}},\mspace{14mu}{v_{2} = \frac{\rho_{1}w_{2}}{{\rho_{2}w_{1}} + {\rho_{1}w_{2}}}}$where ρ₁ and ρ₂ are the mass density of the two components, and w₁ andw₂ are the weight percentage of the two components.

DETAILED DESCRIPTION OF THE INVENTION

The support for the ink jet recording medium used in the invention canbe any of those usually-used for ink jet receivers, such as resin-coatedpaper, paper, polyesters, or microporous materials such as polyethylenepolymer-containing material sold by PPG Industries, Inc., Pittsburgh,Pa. under the trade name of Teslin®, Tyvek® synthetic paper (DuPontCorp.), and OPPalyte® films (Mobil Chemical Co.) and other compositefilms listed in U.S. Pat. No. 5,244,861. Opaque supports include plainpaper, coated paper, synthetic paper, photographic paper support,melt-extrusion-coated paper, and laminated paper, such as biaxiallyoriented support laminates. Biaxially oriented support laminates aredescribed in U.S. Pat. Nos. 5,853,965; 5,866,282; 5,874,205; 5,888,643;5,888,681; 5,888,683; and 5,888,714, the disclosures of which are herebyincorporated by reference. These biaxially oriented supports include apaper base and a biaxially oriented polyolefin sheet, typicallypolypropylene, laminated to one or both sides of the paper base.Transparent supports include glass, cellulose derivatives, e.g., acellulose ester, cellulose triacetate, cellulose diacetate, celluloseacetate propioriate, cellulose acetate butyrate; polyesters, such aspoly(ethylene terephthalate), poly(ethylene naphthalate),poly(1,4-cyclohexanedimethylene terephthalate), poly(butyleneterephthalate), and copolymers thereof; polyimides; polyamides;polycarbonates; polystyrene; polyolefins, such as polyethylene orpolypropylene; polysulfones; polyacrylates; polyetherimides; andmixtures thereof. The papers listed above include a broad range ofpapers, from high end papers, such as photographic paper to low endpapers, such as newsprint. In a preferred embodiment,polyethylene-coated paper is employed.

The support used in the invention may have a thickness of from about 50to about 500 μm, preferably from about 75 to 300 μm. Antioxidants,antistatic agents, plasticizers and other known additives may beincorporated into the support, if desired.

In order to improve the adhesion of the ink-receiving layer to thesupport, the surface of the support may be subjected to acorona-discharge treatment prior to applying the image-receiving layer.

In a preferred embodiment of the invention, the polymeric binderemployed is a hydrophilic polymer such as poly(vinyl alcohol),poly(vinyl pyrrolidone), gelatin, cellulose ethers, poly(oxazolines),poly(vinylacetamides), partially hydrolyzed poly(vinyl acetate/vinylalcohol), poly(acrylic acid), poly(acrylamide), poly(alkylene oxide),sulfonated or phosphated polyesters and polystyrenes, casein, zein,albumin, chitin, chitosan, dextran, pectin, collagen derivatives,collodian, agar-agar, arrowroot, guar, carrageenan, tragacanth, xanthan,rhamsan and the like. In another preferred embodiment of the invention,the hydrophilic polymer is poly(vinyl alcohol), hydroxypropyl cellulose,hydroxypropyl methyl cellulose, gelatin, or a poly(alkylene oxide). Inyet still another preferred embodiment, the hydrophilic binder ispoly(vinyl alcohol).

The particles which may be used in the invention may be organic orinorganic. Examples of such particles include alumina, fumed alumina,colloidal alumina, boehmite, clay, calcium carbonate, titanium dioxide,calcined clay, aluminosilicates, silica, colloidal silica, fumed silica,barium sulfate, or polymeric beads such as vinyl chloride/vinyl acetateor urethane. The particles may be porous or nonporous.

The particles may also be polymeric particles comprising at least about20 mole percent of a cationic mordant moiety useful in the invention canbe in the form of a latex, water dispersible polymer, beads, orcore/shell particles wherein the core is organic or inorganic and theshell in either case is a cationic polymer. Such particles can beproducts of addition or condensation polymerization, or a combination ofboth. They can be linear, branched, hyper-branched, grafted, random,blocked, or can have other polymer microstructures well known to thosein the art. They also can be partially crosslinked. Examples ofcore/shell particles useful in the invention are disclosed and claimedin U.S. patent application Ser. No. 09/772,097, of Lawrence et al.,filed Jan. 26, 2001, the disclosure of which is hereby incorporated byreference.

In a preferred embodiment of the invention, the organic or inorganicparticles have a particle size of from about 0.01 μm to about 0.1 μm,preferably from about 0.03 μm to about 0.07 μm.

Regarding different particles, preferably inorganic particles, thecomposition of the recording medium at which a large dot gain phenomenonoccurs is approximately the same based on the volume percent (comparedto the weight percent) of the particle material. For example, for bothsilica and alumina coatings, the dot gain starts to increase rapidly atabout 50 volume percent of the inorganic material in the recordingelement for both the silica and alumina coatings. Preferably, therefore,the volume percent of the particles is not more than 50 volume percent,more preferably not more than about 45 volume percent, and mostpreferably not more than about 40 volume percent. Regarding thecorresponding dot-gain range, the dot gain is preferably at least 2.5,which is significant for a glossy recording medium in inkjet printingand beneficial to both image quality and printer productivity. Morepreferably, the dot gain is at least 3.0, most preferably 3.5 to 15.

Any cross-linking agent may be used in the invention provided itcross-links the polymeric binder discussed above. The cross-linkingagent may be a carbodiimide, a polyfunctional aziridine, an aldehyde, anisocyanate, an epoxide, a polyvalent metal cation, a vinyl sulfone,pyridinium, pyridylium dication ether, a methoxyalkyl melamine, atriazine, a dioxane derivative, chrom alum or zirconium sulfate.Preferably, the cross-linking agent is dihydroxydioxane.

To improve colorant fade, UV absorbers, radical quenchers orantioxidants may also be added to the image-receiving layer as is wellknown in the art. Other additives include pH modifiers, adhesionpromoters, rheology modifiers, surfactants, biocides, lubricants, dyes,optical brighteners, matte agents, antistatic agents, etc. In order toobtain adequate coatability, additives known to those familiar with suchart such as surfactants, defoamers, alcohol and the like may be used. Acommon level for coating aids is 0.01 to 0.30 percent active coating aidbased on the total solution weight. These coating aids can be nonionic,anionic, cationic or amphoteric. Specific examples are described inMCCUTCHEON's Volume 1: Emulsifiers and Detergents, 1995, North AmericanEdition.

Ink jet inks used to image the recording elements employed in thepresent invention are well-known in the art. The ink compositions usedin ink jet printing typically are liquid compositions comprising asolvent or carrier liquid, dyes or pigments, humectants, organicsolvents, detergents, thickeners, preservatives, and the like. Thesolvent or carrier liquid can be solely water or can be water mixed withother water-miscible solvents such as polyhydric alcohols. Inks in whichorganic materials such as polyhydric alcohols are the predominantcarrier or solvent liquid may also be used. Particularly useful aremixed solvents of water and polyhydric alcohols. The dyes used in suchcompositions are typically water-soluble direct or acid type dyes. Suchliquid compositions have been described extensively in the prior artincluding, for example, U.S. Pat. Nos. 4,381,946; 4,239,543 and4,781,758, the disclosures of which are hereby incorporated byreference.

The following examples are provided to illustrate the invention.

EXAMPLES Example 1

Control Element C-1 (Greater Than 65 Vol. % Particles)

A coating solution for the image-receiving layer was prepared bycombining 28.10 g/m² of fumed alumina particles, Cabosperse PG-033®(Cabot Corp.), 2.9 g/m² of poly(vinyl alcohol), Gohsenol® GH-23A (NipponGohsei Co.), and 1.3 g/m² of dihydroxydioxane (DHD) cross-linking agent.The weight ratios of these materials are 87%, 9% and 4%, respectively.

The layer was bead-coated at 40° C. on polyethylene-coated paper base,which had been previously subjected to corona discharge treatment. Thecoating was then dried at 60° C. by forced air in which the thickness ofthe image-receiving layer was 30 μm.

Element 1 of the Invention

This element was prepared the same as C-1 except that the weight ratiosof the materials were 76%, 20% and 4% respectively.

Element 2 of the Invention

This element was prepared the same as the C-1 except that the weightratios of the materials were 66%, 30% and 4% respectively.

Element 3 of the Invention

This element was prepared the same as the C-1 except that the weightratios of the materials were 56%, 40% and 4% respectively.

Element 4 of the Invention

This element was prepared the same as the C-1 except that the weightratios of the materials were 46%, 50% and 4% respectively.

Control Element C-2 (Less Than 20 vol. % Particles)

This element was prepared the same as the C-1 except that the weightratios of the materials were 36%, 60% and 4% respectively.

Control Element C-3 (Less Than 20 vol. % Particles)

This element was prepared the same as C-1 except that the weight ratiosof the materials were 26%, 70% and 4% respectively.

Control Element C-4 (Less Than 20 vol. % Particles)

This element was prepared the same as C-1 except that the weight ratiosof the materials were 16%, 80% and 4% respectively.

Control Element C-5 (Less Than 20 vol. % Particles)

This element was prepared the same as C-1 except that the weight ratiosof the materials were 6%, 90% and 4% respectively.

Control Element C-6 (Less Than 20 vol. % Particles)

This element was prepared the same as C-1 except that the weight ratiosof the materials were 0%, 96% and 4% respectively.

Dot Gain

Test images of cyan drops were printed on the above elements using atypical ink jet print head using the Cyan Ink Composition describedbelow. The drop volume was 16.7 pL corresponding to a drop diameter of31.7 μm. The resulting dot size was measured relative to the dropdiameter and the dot gain or spread factor is reported in Table 1.

Cyan Ink Composition

The cyan ink contained 2% Direct Blue 199 dye, 40% diethylene glycol,25% diethylene glycol monobutyl ether, and the balance water. Theviscosity and surface tension of the ink are 8.4 cP and 33 dyne/cm,respectively.

TABLE 1 Alumina/PVA/DHD Volume % of Coating Dot Element (wt. %) AluminaWeight (g/m²) Gain C-1 87/9/4 66.8 32.3 2.1 1 76/20/4 48.7 32.3 2.9 266/30/4 36.8 32.3 12.6 3 56/40/4 27.6 32.3 14.7 4 46/50/4 20.4 26.9 14.6C-2 36/60/4 14.4 26.9 12.6 C-3 26/70/4 9.54 21.5 9.2 C-4 16/80/4 5.4121.5 7.4 C-5  6/90/4 1.88 21.5 6.9 C-6  0/96/4 0.00 21.5 4.7

The above results show that the Elements of the Invention have asubstantially greater Dot Gain than the Control Element C-1 which hadgreater than 65% by volume of particles. While Control Elements C-2,C-3, C-4, C-5 and C-6 had improved Dot Gain as compared to C-1, theseelements would not be porous and would have the disadvantages discussedpreviously. When a high dot gain medium is used for printing, the inkshould have a higher concentration of colorant (directly proportional tothe dot gain of the medium) in order to achieve the same image densityas a nominal dot gain medium.

Example 2

This Example was the same as Example 1 except that the support wastransparent poly(ethylene terephthalate), the particles were fumedsilica, Cabosperse PG-001® (Cabot Corp.), the coating weight was 32.3g/m², the thickness of the image-receiving layer was 30 μm, the dropdiameter was 31.3 μm (16.0 pL) and the ink composition was a black inkcomprising Reactive Black 31 black dye, glycerol, diethylene glycol,butoxytriglycol and water. The viscosity and surface tension of the inkare 3.0 cP and 38 dyne/cm, respectively. Elements 7 through 13 andControl Element C-7 were prepared using the amounts shown in Table 2below. The following results were obtained:

TABLE 2 Element Silica/PVA/DHD (wt. %) Volume % of Silica Dot Gain  765/31/4 50.3 2.3  8 60/36/4 45.0 2.7  9 55/41/4 40.0 3.5 10 50/46/4 35.37.6 11 45/51/4 30.9 7.9 12 40/56/4 26.7 7.5 13 35/61/4 22.7 4.3 C-730/66/4 19.0 4.2

The above results show that the Elements of the invention using silicaand a transparent support of the invention have a significant Dot Gain.While C-7 had improved Dot Gain, this element would not be porous andwould have the disadvantages discussed previously

Although the invention has been described in detail with reference tocertain preferred embodiments for the purpose of illustration, it is tobe understood that variations and modifications can be made by thoseskilled in the art without departing from the spirit and scope of theinvention

1. A method of inkjet printing comprising applying an ink jet ink drophaving a viscosity of about 2.5 to about 8.5 cP and a surface tension ofabout 25 to 45 dyne/cm to the surface of porous ink jet recording mediumcomprising a support having thereon an image-receiving layer, saidimage-receiving layer containing: a) from about 20 to about 50% byvolume of or inorganic or organic particles, said inorganic or organicparticles having a particle size of from about 0.01 μm to about 0.1 μm;b) from about 25 to about 70% by volume of a polymeric binder; and c) upto about 10% by volume of a cross-linking agent; whereby the diameter ofsaid ink jet ink dot is increased relative to that which would have beenobtained if said image-receiving layer had greater than about 50% byvolume of said inorganic or organic particles, wherein the dot gain is2.5 to
 15. 2. The method claim 1 wherein said organic or inorganicparticles comprise alumina, fumed alumina, colloidal alumina, boebmite,clay, calcium carbonate, titanium dioxide, calcined clay,aluminosilicates, silica, colloidal silica, fumed silica, bariumsulfate, vinyl chloride/vinyl acetate or urethane.
 3. The method ofclaim 1 wherein said organic or inorganic particles have a particle sizeof from about 0.03 μm to about 0.07 μm.
 4. The method claim 1 whereinsaid polymeric binder comprises poly(vinyl alcohol), hydroxypropylcellulose, hydroxypropyl methyl cellulose, gelatin, or a poly(alkyleneoxide).
 5. The method of claim 1 wherein said polymeric binder isgelatin or poly(vinyl alcohol).
 6. The method of claim 1 wherein saidcross-linking agent comprises a carbodiimide, a polyfunctionalaziridine, an aldehyde, an isocyanate, an epoxide, a polyvalent metalcation, a vinyl sulfone, pyridinium, pyridylium dication ether, amethoxyalkyl melamine, a triazine, a dioxane derivative, chrom alum orzirconium sulfate.
 7. The method of claim 1 wherein said cross-linkingagent comprises dihydroxydioxane.
 8. The method of claim 1 wherein saidsupport is polyethylene-coated paper.
 9. The method of claim 1 whereinsaid ink jet ink drop comprises a dye dispersed in water.
 10. A methodof inkjet printing comprising an ink jet ink drop having a viscosity ofabout 2.5 to about 8.5 cP and a surface tension of about 25 to 45dyne/cm to the surface of porous ink jet recording medium comprising asupport having thereon an image-receiving layer, said image-receivinglayer containing: a) from about 20 to about 45% by volume of inorganicor organic particles, said inorganic or organic particles having aparticle size of from about 0.01 μm to about 0.1 μm; b) from about 25 toabout 70% by volume of a polymeric binder; and c) up to about 10% byvolume of a cross-linking agent; whereby the diameter of said ink jetink dot is increased 3.0 relative to that which would have been obtainedif said image-receiving layer had greater than about 45% by volume ofinorganic or organic particles, wherein the dot gain is 3.0 to
 15. 11.The method of claim 10 wherein the image-receiving layer comprises notmore than 40% by volume of particles and the dot gain is 3.5 to 15.